Q.4 Sodium – Potassium ATPase transports

(1) 3 Na⁺ In and 2 K⁺ Out of the cell

(2) 2 K⁺ In and 3 Na⁺ Out of the cell

(3) 3 K⁺ In and 2 Na⁺ Out of the cell

(4) 2 K⁺ Out and 2 Na⁺ In of the cell

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The Sodium-Potassium ATPase (Na+/K+ pump) is an active transport protein maintaining electrochemical gradients across cell membranes. Grasping what Sodium Potassium ATPase transports is fundamental for physiology, cell biology, and exam success.

Correct Answer: Option (2) 2 K+ In and 3 Na+ Out of the cell

This pump uses ATP hydrolysis to move 3 sodium ions (Na+) out of the cytosol against their gradient and 2 potassium ions (K+) into the cell, also against their gradient. The cycle involves E1 (cytosolic, Na+-binding) and E2 (extracellular, K+-binding) conformations with phosphorylation/dephosphorylation steps.

Example: In neurons, it restores resting potential (-70 mV) after action potentials by countering Na+ influx and K+ efflux.

This electrogenic action (net +1 charge out) sustains cell volume and excitability.

Why Other Options Are Incorrect

• Option (1) 3 Na+ In and 2 K+ Out of the cell
  Reverses the pump’s direction; this would depolarize cells and collapse gradients, opposite to its physiological role.

• Option (3) 3 K+ In and 2 Na+ Out of the cell
  Wrong stoichiometry—pump exchanges 3 Na+ for 2 K+, not 2 Na+ for 3 K+; K+ entry supports, doesn’t overwhelm, the gradient.

• Option (4) 2 K+ Out and 2 Na+ In of the cell
  Equal 1:1 exchange lacks electrogenicity and doesn’t match 3:2 ratio; resembles passive leak channels, not active pump.

Transport Summary Table

Understanding Sodium Potassium ATPase transports clarifies nerve impulses, muscle contraction, and osmoregulation.